Field of the Invention
The present invention relates to cellulose nanofibres, a bio composite resin composition and a method for producing a bio composite resin composition. Particularly, the present invention relates to chemically modified cellulose nanofibres, a bio composite resin composition comprising a matrix of nanofibrillated surface-modified cellulose (NFC) and polyvinyl alcohol (PVOH), a method for producing NFC-PVOH bio composite resin composition, a casting-sheet bio composite body and a use thereof for producing biodegradable composites.
Description of Related Art
Cellulose is one of the most abundant biopolymers in nature, and it has been modified in several ways to overcome the difficulties experienced in compatibility. Nanofibrillated cellulose (NFC) is a new potential building block for bionanocomposites, which offers further means for biopolymer modification and interesting new qualities, such as a highly reactive surface and the opportunity to make lighter, strong materials with greater durability. NFC displays high stiffness and strength, and its hydroxyl groups offer reactive sites for chemical modification. Furthermore NFC is attractive reinforcing filler in thermoplastic matrix materials due to its low density, biodegradability, renewability, low cost and gas barrier properties.
Nanocellulose has been used for composite materials in the prior art. For example, Chinese patent CN 10240861 B describes a high barrier nanocellulose composite material and its preparation method. However, the material described comprises 0.2 wt-% to 10 wt-% of unmodified nanocellulose, which is introduced into a poly fatty acid ester material.
Among the biofibre-reinforced polymer composites the major challenge has been the incompatibility of fibres to polymer matrix. Generally that is why the biopolymer based films are limited in their ability to obtain wide commercial application due to disadvantages in mechanical properties and brittleness.
Chemical modification of the fibres is a large research area that currently investigates how to improve compatibility of fibres in matrix polymer. Different chemical surface modification methods of cellulose have been published (Stenstad et al. 2008; Cai et al. 2003; Wu et al. 2000). One of the most promising means of modification has been to introduce functional epoxy groups into the biopolymer structure surface. Epoxy groups serve as capable cross-linkers and additionally bind to polyamines, peptides and amino acids (Arola et al. 2012; Bai et al. 2006; Huijbrechts et al. 2010). Epoxy groups have been introduced into the biopolymer surface using direct epoxidation methods (Burton and Harding 1997; Tomasik and Schilling 2004). The drawbacks using these methods have been the use of hazardous materials and various side reactions.
However, it is also possible to prepare epoxy cellulose by using allyl cellulose as an intermediate product. Allyl cellulose is a derivative that offers a pathway for various subsequent reactions due to the high reactivity of the allyl double bonds (Heinze et al. 2008; Lin and Huang 1992; Mu-Shih and Chung-Song 1992). Epoxy cellulose can alternatively be prepared by oxidizing the allyl double bonds and such a procedure has been previously described for starch (Huijbrechts et al. 2010) and cellulose fibres (Arola et al. 2012). However, the methods described in the articles have limitations and high degree of substitution is not achievable.
Patent application JP 2011184816 A relates to surface-modified cellulose nanofibres and a composite resin composition thereof. In this Japanese application surface modification has also been carried out to hydroxyl groups of cellulose fibres. However, the used modification method has limitations and, among others, results in lower degree of surface modification.
WO 2012/127119 relates to a method for producing a bio composite resin composition and its use for producing biodegradable compositions. However, the products obtained are still limited in their ability to obtain wide commercial application because of their inadequate mechanical properties and brittleness.
Use of nanocellulose to reinforce a polyvinyl alcohol matrix has also been studied in the prior art. For example, Hu et al. (2012) describe reinforced polyvinyl alcohol (PVA) with nanocellulose fibrils generated from poplar and cotton with mechano-chemical treatment (acid/alkali treatment enhanced with grinding). In this article researchers have produced PVA/nanocellulose composite by an immersion method followed by drying the solution. However, the nanocellulose fibrils are not chemically modified, resulting in a certain incompatibility of the fibres to polymer matrices.
Bionanocomposites or bio-based nanocomposites are materials made from renewable materials with at least one component having a dimension smaller than 100 nm (e.g., microfibrillated cellulose, MFC, or nanocellulose, NFC). Polymer composites include a polymer matrix component, common examples being petroleum-derived polymers such as polypropylene (PP) and polyethylene (PE). These polymer nanocomposites contain low quantities of well-dispersed nano-sized fillers to obtain high mechanical performance (Siqueira et al. 2010). The properties of the resulting polymer nanocomposites are therefore not ideal, because adhesion between e.g. nanocellulose fibres and matrix polymer is weak and fibre dispersion to polymer material needs improvement.
Currently, there is an increasing global demand for biodegradable plastic resins and environmentally sustainable bio composite products. Consequently, the price of suitable raw materials for use in preparing the composites, such as polyvinyl alcohol, is increasing. By utilizing epoxidized nanofibrillated cellulose as filler in e.g. polyvinyl alcohol matrix it is possible to reduce the amount of polyvinyl alcohol and produce new composite materials to different market sectors. Hence, the present invention provides new value-added and biodegradable PVOH-based composites.